Variable venturi type carburetor



Jan. 16, 1945.

M. J. KITTLER 2,367,507 4 VARIABLE VENTURI TYPE CARBURETOR Filed NOV. 16, 1942 INVENTOR.

@atented Jan. 16, 1945 VARIABLE VENTURE TYPE CARBURETOR Milton J. jKittler, Detroit, Micln, assignor to George M. Holley and Earl Holley Application Novemher is, 1942, Serial No. assets 2 Claims. (or. 261-50) The object of this is to improve the operation of that form of airplane engine carburetor known as the pressure type. In this type of-carburetor, fuel under pressure is discharged on the engine side of the throttle and the flow is regulated by the depression in the venturi located on the atmospheric side of the throttle. Obviously at low air flows, the depression of the venturi is very weak. Hence, the regulation of the fuel is most uncertain. In order to overcome this, I have combined the throttle with the venturi and utilized the variable venturi so formed for the creation of the necessary suction for metering the fuel.

Obviously, at closed throttle, the suction is then at a maximum. Hence, the fuel metering orifice must be reduced with the variable venturi.

The figure show-s diagrammatically the elements of my invention. ill is the air entrance, ii and ii are the two elements of the variable venturi. l3 and M are two gears interconnecting the two elements it and H2. The gear it engages with a gear it mounted on the shaft llon which is mounted a cam i8. The roller l9 mounted on the lever 2t engages with the surface of the cam is. A spring 28 holds the roller l9 in engagement with the cam surface IS. A needle 22 known as.

the metering pin is moved by the lever and controls an orifice 23 which is the main fuel metering orifice, Obviously, as, cam l8 rotates anticlock-.

wise, the element l2 rotates clockwise and the element ll anticlockwise. opens the orifice 23 inproportion as the elements l l and i2 open the variable venturi which is formed between them. The rate of flow through the orifice 23 is controlled by the pressure difference to the right and left of this orifice. The pressure in the chamber 24 is determined by the opening of the fuel inlet valve 25 to which fuel is supplied by the pump 26. The pressure difierence of the pump 26 is maintained substantially constant by means of a pressure release valve 21. I'he valve 25 is regulated by the action of the lever 3| which is connected with the diaphragm and 33 through the rod 32. The fuel passes the oi iflce 23 and flows to a spring loaded discharge? ozzle 28 located in the air inletv passage downstream from'the variable Venturi throttles H and-l2.

.The pressure on the downstream side ofthe orifice 23 is communicated through an open passage to chamber}! and through to the diaphragm 30.

The diaphragm 30 is located between the chamhers retina 2s.- The rod 32 connects the dia- Thus the needle 22' phragm iifl with a corresponding diaphragm 33.

These two diaphragms therefore are thus rigidly connected with each other. Diaphragm arates an air chamber into two halves 3d and 37. The chamber 34 is in communication with the air entrance It] through a passage 35 and vent ring 36. Substantially atmospheric pressure exists therefore in the chamber 34. Chamber 3'! at the right of diaphragm 33 communicates through the passage 38, passage 39 opening 48 with the throat of the variable venturi i l-l2. The diaphragm 3d on the other end is responsive to the pressure difference of thefuel flowing through the orifice 23. The fuel and air flows are maintained proportional because the difference of pressure created by the flow of fuel past the needle valve 22 balances the diilerence of pressure created by the flow of air through the venturi 12. Both diiferences of pressure normally vary as the square. of the velocity of flow. Hence, we have in its simplest possible form, a method of balancing air flow with fuel flow. It is necessary, however, to provide means to:

(A) Adjust for idle.

(B) Vary the mixture ratio. (C) Control for altitude. (D) Shut off the fuel.

A. A bypass 42 leads from the chamber 24 to the discharge nozzle 28 and the needle valve 4! regulates the flow.

B. The mixture control link 43 controls a lever C. To control the mixture ratio at altitude evacuated elements 41 located in a chamber 48 (which is maintained at an atmospheric pressure throuzh Openings 49) control a valve 50 which at high altitude admits more air to the passage 5|, which passage BI is an extension of the passage 33. In other words, atmospheric pressure is admitted to the chamber 31. The'opening past the valve 5!) is not large enough to destroy the suctionat the openings 40. Hence the valve 50 can never admit atmospheric pressure in the chamber 31, and there will always be a depression in the chamber 31 which depression will vary with the .alr flow past the orifice ll.

1:. Obviously, it the link 4: lsmoved all the way down, "the valve 25 can not open and there 33 sep 56 be a complete 830998-88 of the fuel.

Operation When operating at sea level with the throttle closed, the barometric element 41 causes the valve 30 to restrict the admission of atmospheric air to the passage 5|. The result is that, the depression in the chamber 31 is substantially that existin in the throat of the variable venturi and the pressure in the chamber 34 is substantially atmospheric pressure. Hence, the diaphragm 33 is pushed to the right by the diflerence in pressure between the pressure in the throat of the venturi and the atmospheric pressure. This causes the rod 32 to move to the right which permits the fuel valve 25 to open and thus admit fuel under pressure to the chamber 24 which flows out past the needle valve 22 creating an increased pressure drop across the fuel orifice 23. This increased pressure drop causes a lower pressure in the chamber 29 relative to the pressure in the chamber 24. This increased pressure drop causes the rod 32 to move to the left, hence the two diaphragms 30 and 33 are maintained in equilibrium. As the throttles H, l2are opened the orifice 22 also opens and the same proportional flow is maintained. At altitude the barometric element 41 expands and atmospheric air is admitted to passage 5| and therefore the flow of fuel is reduced by the atmospheric air entering the passage 5|. Hence the tendency for the fuel to become richer is corrected.

What I claim is:

1-. In a carburetor of the pressure type, an air entrance air throttling means therein of the variable Venturi type, a fuel supply system adapted to supply fuel under pressure, a fuel entrance chamber, a valve admitting fuel under pressure to said chamber, a fuel outlet, a movable restriction therein connected to said air throttling means so that the fuel outlet increases with the opening of the variable venturi, a second fuel chamber communicating with the fuel on the downstream side of said fuel restriction, said first and second chambers having a diaphragm which forms a common wall therebetween, a corresponding pair of air chambers having a diaphragm which form a common wall therebetween, a passage connecting the 1st of said air chamhers with the air entrance, a passage connecting the 2nd of said chambers with the throat of said variable venturi, linkage connecting said fuel diaphragm and said air diaphragm together and with said fuel entrance valve whereby an increase in the air flow tends to open the fuel entrance valve and an increase in fuel flow tends to close the fuel entrance valve.

2. A device as set forth in claim 1 in which there is a barometric responsive air valve located in the air entrance, said valve adapted t admit air under atmospheric pressure to the passage leading to the 2nd of said air chambers so as to reduce the pressure difference between said air chamber at high altitudes-and thus reduce the fuel flow.

MILTON J. KIT'I'LER. 

